Exhaust stack



FIG. 1 is a front perspective view of an exhaust stack showing inventor's new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view;

Portions of the exhaust stack shown in broken lines in FIG. 7 are environment and form no part of the claimed design. 

I claim the ornamental design for an exhaust stack, as shown and described. 